This invention relates to an apparatus by means of which the position and size of silicon crystals may be determined at machined surfaces of an Al-Si alloy from which e.g. cylinder sleeves or motor blocks for automotive vehicles are made.
The silicon crystals represent supporting points along which the light-metal piston slides. The size and the distribution of these supporting points on the peripheral surface of the cylinder have a decisive effect on the life of the motor and should therefore be tested at each motor block. The metallographic and optical methods used up to now are suited for laboratory measurements, but are too costly and too time-consuming for production. The scanning intersection methods used for surface testing are just as unsuited as light intersection and interference microscopes because the surface structure in the region of the aluminum and in the region of the silicon crystals has no systematic differences which are able to be detected with these methods.
Thus, the appartus known up to now cannot be used for detecting silicon crystals.